Atrial natriuretic peptide (ANP) is the first described peptide in a family of hormones which regulate body fluid homeostasis (see Brenner et al., 1990). The description of the potent diuretic and natriuretic properties of atrial extracts by de Bold et al. (1981) was the first evidence that the heart could be an endocrine organ. The subsequent isolation and characterization of this activity by groups including Flynn et al. (1981) characterized ANP as the first secreted cardiac hormone. ANP is secreted by atrial myocytes in response to increased intravascular volume. Once it is in the circulation, its effects are primarily on the kidney, vascular tissue, and adrenal gland, in which its actions lead to the excretion of sodium and water by the kidneys and a decrease in intravascular volume and blood pressure (Atlas et al., 1987).
Matsuo and his coworkers isolated two other natriuretic peptides. Brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) were both isolated from porcine brain extracts on the basis of their potent relaxant effects on chick rectum (Sudeh et al., 1988; Sudeh et al., 1990). BNP is of myocardial cell origin, and like ANP circulates in human plasma (de Bold et al., 1981; Burnett et al., 1984). BNP is natriuretic, renin inhibiting, vasodilating, and lusitropic (Mukoyama et al., 1991; Yamamoto et al. 1996; Grantham et al., 1996). CNP is of endothelial cell origin and functions as a vasodilating and growth-inhibiting peptide (Suga et al., 1992; Stingo et al., 1992; Koller et al., 1991). ANP and BNP are increased in the plasma and heart during congestive heart failure (CHF) in humans, and they exert important cardiorenal protective actions in addition to serving as serum markers for ventricular dysfunction (Stevens et al., 1995; Yamamoto et al., 1997; McDonagh et al., 1998).
ANP, BNP and CNP are synthesized from large precursor proteins, and the mature, active peptides have a 17 amino acid loop formed by an intramolecular disulfide linkage. In the human peptides, eleven of these amino acids are identical in ANP, BNP, and CNP, whereas the N- and C-terminal tails vary in both length and composition (see Kambayashi et al., 1990; and Tawaragi et al., 1991). CNP has no C-terminal tail, and studies of the structure of the gene for CNP demonstrated that translation is terminated by a stop codon immediately after the final cysteine codon in the mRNA.
Among species, the amino acid sequence of both ANP and CNP are highly conserved, whereas the structure of BNP varies greatly. For example, the mature 28 amino acid human and porcine ANPs are identical, and there is only one substitution in the rat peptide. The existence of this structural variation, coupled with the presence of at least three types of receptors specific for the natriuretic peptides, suggests that the physiological control of body fluid homeostasis is complex. ANP and CNP both decrease cardiac preload. However, unlike ANP, CNP is not natriuretic (Stingo et al., 1992).
The diverse actions of ANP, BNP and CNP on both the cardiovascular system and the kidney, as well as their roles in pathophysiological states such as heart failure, hypertension, and renal disease, have made the native peptides and their analog molecules of great interest to both clinical and basic scientists. See, for example, Lewicki et al. (U.S. Pat. Nos. 5,114,923, 4,804,650 and 4,757,048), Johnson et al. (U.S. Pat. No. 5,047,397) and Johnson et al. (U.S. Pat. No. 4,935,492), and Wei et al. (U.S. Pat. No. 5,583,108). U.S. Pat. No. 5,583,108 relates to a chimera of ANP and CNP, termed vasonatrin peptide (VNP). VNP, which includes 22 amino acids of CNP and the 5 amino acids at the carboxy-terminus of ANP, has arterial and venous vasodilating and natriuretic effects.
A fourth natriuretic peptide (NP), Dendroaspis natriuretic peptide (DNP), possesses structural similarity to ANP, BNP, and CNP. Isolated from the venom of Dendroaspis angusticeps or green mamba snake, DNP is a 38 amino acid peptide that contains a 17 amino acid disulfide ring structure similar to that of ANP, BNP, and CNP (FIG. 1), all of which mediate biologic actions through particulate guanylyl cyclase receptors and generation of cyclic guanosine monophosphate (cGMP) (Schweitz et al., 1992). DNP vasorelaxes rodent aorta and isolated canine coronary arteries with potency comparable to that of ANP (Schweitz et al., 1992; Wennberg et al., 1997). Additionally, DNP substantially augments the formation of cGMP, the second messenger for the other natriuretic peptides, in aortic endothelial cells (Schweitz et al., 1992).
Thus, there is a continuing need to identify peptides with properties such as those of natriuretic peptides which are useful to prevent or treat cardiovascular disorders, e.g., congestive heart failure.